NL9400534A - System for determining a composition of radionuclides. - Google Patents

Description

Title: System for determining a composition of radionuclides.

The invention relates to a system for determining a composition of radionuclides in, for example, a mineral-containing matter by detecting gamma and / or X-rays emitted by the nuclides, provided with a detector unit which emits an electrical signal containing information about the intensity and energy of the emitted radiation and a signal processing system with which these electrical signals are further processed for determining said composition.

Such systems are known per se and are used, inter alia, for the exploration and exploitation of oil and gas. This method is based on the presence of radionuclides in minerals. These nuclides emit radiation that is characteristic of the nuclide in question. By detecting this radiation, information can be obtained about the composition of nuclides in minerals.

The interesting nuclides to be detected are long life nuclides (half-life of more than 109 years) such as, for example, 40k, 232Th, 235h and 238h and their decay products. During the period when minerals were formed, these nuclides are included. The concentration of these nuclides in the minerals strongly depends on the type of mineral. These concentrations are therefore often characteristic of the type and location of minerals.

The radionuclides mentioned often decay into a stable lead isotope via a long series of intermediates. Alpha, beta, gamma and X-rays can be released during this radioactive decay. However, the present invention only relates to detecting and interpreting emitted gamma and X-rays.

In the known systems, the radiation to be detected is dropped, for example, on a crystal, whereby a light flash can be generated. In the case of gamma and X-rays, such a photon causes such a flash of light.

These flashes of light are fed to a photomultiplier that converts the weak flashes of light into electrical pulses. The magnitude of the electric pulse is a measure of the energy of the photon incident on the crystal.

By counting the number of pulses and sorting them by pulse height over a period of, for example, twenty seconds, an energy spectrum can be composed, that is, the number of photons registered per unit time as a function of their energy.

In such a spectrum there will be peaks or lines which are caused at least essentially by the radionuclides mentioned, respectively. A peak or collection of peaks can then be attributed to a nuclide. In addition, however, contributions from other physical phenomena are present in the spectrum, such as the Compton effect.

In the known systems, the spectrum is analyzed per window. A peak is present within a window. That is, the contents of generally three windows are determined. The contents of these windows can be used to determine which nuclides have been detected. The information about the contents of the windows is then processed in combination with each other to determine the concentrations of the nuclides in the material in question. After all, the concentrations of the nuclides appear to have an almost linear relationship with the intensity of the radiation, that is, with the number of emitted photons.

In these systems use is often made of Nal (Tl) crystals; such a crystal has a moderate energy resolution and is furthermore insensitive to high energy radiation, so that a long integration time, for example more than 20 seconds, is required to obtain a usable spectrum.

The object of the invention is to obviate said disadvantage of low sensitivity by, on the one hand, preferably using a crystal with greater sensitivity and, on the other hand, to involve as much as the total energy spectrum in the analysis. The object of the invention is moreover to provide a system in which, if desired, correction can also be made for other influences, such as, for example, temperature variations, etc.

According to the invention, the signal processing system is for this purpose provided with an a / D converter to which said electrical signals are supplied and a first computer unit which further processes signals output by the A / D converter for determining said composition. Because the spectrum is composed by the computer unit and subsequently analyzed by the computer, it is easy to correct for said effects.

According to a preferred embodiment, the detector unit comprises a scintillation detector and a photomultiplier that converts the light pulses delivered by the scintillation detector into an electric pulse with an amplitude that is a measure of the energy of the radiation received by the scintillation detector. The detector is herein preferably provided with a pulse height analyzer for obtaining said electrical signals from the electrical pulses.

However, according to the invention it is also possible to use other detector units. Such an alternative detector unit may comprise a semiconductor crystal to which a bias voltage is applied and means for detecting a variation in the bias voltage to obtain said electrical signals.

According to a particular aspect of the invention, the first computer unit composes an energy spectrum of the detected radiation from the signals supplied by the A / D converter, in particular the first computer unit determines the spectrum according to a predetermined first algorithm concentration of the radionuclides.

According to a very advantageous embodiment, the first computer unit determines said concentrations on the basis of the completely determined spectrum. By using all available information, i.e. the full spectrum, according to this method, very high accuracy is obtained. According to the previously known per se known method in which the content of only three windows is analyzed, only about 10 percent of the available information is processed.

According to the invention, the detector unit is preferably provided with a BGO crystal. The sensitivity of such a crystal to high energy radiation is much better (an order of magnitude) than the sensitivity of a conventional Naï (Tl) crystal. However, the energy resolution is slightly less good than with the Nal (Tl) crystal, so the energy spectrum will include slightly wider peaks. The peaks will therefore overlap more. Due to the fact that the spectrum is analyzed with said predetermined algorithm, reliable information can still be obtained from the spectrum.

According to another aspect of the invention, the first computer unit determines the composition of the matter in minerals on the basis of said concentrations according to a predetermined second algorithm.

According to still another aspect of the invention, the first computer unit is provided with a memory in which energy spectra of radiation emitted by radionuclides are stored. These in-memory stored spectra can be used in the predetermined first algorithm. Likewise, the memory of the computer may contain data of minerals known per se and the associated concentrations of radionuclides. This information stored in memory can be used in the second algorithm.

According to a very advanced embodiment of the invention, the detector unit is provided with sensors with which sound, temperature, magnetism and / or other physical phenomena in the vicinity of the nuclides to be detected can be detected and converted into an electrical sensor signal. The sensor signal can be supplied via the A / D converter to a computer unit, such as, for example, the first computer unit, for making corrections when determining said composition.

In addition, it is possible that the sensor signal is applied to a second computer unit to correct and / or stabilize the detector unit.

This makes it possible to separate the detector unit and the first computer unit, whereby the said corrections can be carried out directly locally at the detector unit.

for example, it is possible that the system further includes a transmitter unit to which output signals from the A / D converter are applied and a receiver unit which supplies received signals to the first computer unit. The detector unit and the a / d converter are herein housed, for example, in a probe-forming housing. Such a probe can be used in many places.

In this connection it is noted that the system according to the invention is applicable in many areas, for example the system can be used for measuring and / or analyzing sludge, separating minerals in, for example, waste processing and tracing waste flows in rivers and oceans. . In addition, the system detector unit can also be mounted under an aircraft to perform radiometric tracing. Another example, however, is the conducting of horizontal and / or vertical soil investigations, the conducting of soil analyzes and the aforementioned exploration and exploitation of minerals.

The invention will be further elucidated with reference to the drawing. Herein: figure 1 shows an embodiment of a system according to the invention; figure 2 shows an example of an energy spectrum of a mineral; and Figure 3 shows the process steps performed by the system according to Figure 1.

In Figure 1, reference numeral 1 shows a system for detecting and interpreting gamma and X-rays emitted by radionuclides according to the invention. The system is provided with a scintillation detector 2 known per se: in this example a BGO (Bismuth Germanium Oxide) crystal. This crystal can generate a flash of light when a photon of the radiation falls on the crystal. These light flashes are supplied, as schematically indicated by reference numeral 4, to a known type of photomultiplier 6. The photomultiplier 6 converts the light pulses delivered by the scintillation detector into an electric pulse with an amplitude which is a measure of the energy of the radiation received by the scintillation detector. These electric pulses are supplied via line 8 to a known type of pulse height analyzer 10.

The pulse height analyzer generates electrical signals on line 12 which contain information about the height of a pulse and hence the energy delivered by the photons. This analyzer 10 consists, for example, of a detection device (not shown here) which emits a signal when a pulse is present and a sample and hold device (also not shown) to which the output signal of the latter detection device is applied. detected photons (cps) is a measure of the intensity of the radiation, so that this information is also present in the electrical signal on line 12.

The said electrical signal is then fed to an A / D converter 14 which digitizes the signal.

The digitized signal in this example is then supplied via line 16 to a transmitter / receiver unit 18 which transmits the digitized signal. The carrier wave modulated with the electrical signal is indicated schematically by reference numeral 20.

In this example, the system is further provided with a transmitter / receiver unit 22 for receiving and demodulating the signal transmitted by the transmitter / receiver unit 18. The transmitter / receiver unit 22 provides a digital signal on line 24 corresponding to the digital signal output from the A / D converter.

The digital signal is then fed to a first computer unit 26 for further processing. The computer unit 26, in a manner known per se, composes an energy spectrum from the digital information, as shown by way of example in Figure 2.

In this example, for a period of about one second, the first computer unit 26 counts the number of pulses of a magnitude between Ei + 1 and Ei for i = 1, l, ... n with n = En-Eo / Ei + i -Egg. If n is large, a substantially continuous spectrum can be constructed as shown in Figure 2. Figure 2 shows three peaks originating from K, u and Th.

On the basis of spectra originating from pure K, U, and Th, respectively, and which are stored in a memory 28 of the first computer unit 26, the spectrum of Figure 1 is deconvolved according to a first algorithm to obtain the concentrations of the detected detected isotopes in, for example, a material that contains various minerals. Preferably, the algorithm uses the entire spectrum for this purpose, i.e. all the information that is available.

memory 28 also stores data about known minerals and the concentrations of the isotopes contained therein. The computer 26 then determines on the basis of this data and the measured concentrations according to a second algorithm in what ratio the groups of minerals have been detected. This data is then passed to a data output system 30 for further processing. According to this method, a new spectrum can therefore be determined and analyzed every second or as much longer as desired.

On the basis of spectra determined by the first computer unit 26, certain parameters with which, for example, the photomultiplier 6, the pulse height analyzer and the A / D converter can be adjusted, can then be adjusted. Feedback is then generated to the photomultiplier 6, the pulse height analyzer and / or the A / D converter 14. The feedback signals generated by the computer unit 26 can be fed via line 24, transmitter / receiver units 22, 18 and line 16 to the A / D converter. The system further includes a D / A converter to feed these feedback signals through lines 12 and 8 to the photomultiplier 6 and the pulse height analyzer 10. For example, if the amplification factor of the signal is not optimal, the gain of one of these parts 6,10 and / or 14 can be adjusted in this way.

According to a special embodiment of the system, the system is further provided with additional sensors. In this example, two such sensors 32,34 are shown. However, it is also possible to expand the system with three or more sensors. In this example, the sensor 32 is a temperature sensor. The temperature-representing signals output from this sensor 32 are fed via line 36 to the A / D converter. The A / D converter digitizes this signal and sends it via line 16 to the transmitter / receiver unit. In this case, it is ensured, for example, via multiplexing techniques or coding techniques that these signals on line 16 are distinct from signals originating from the pulse height analyzer. The first computer unit 26 can then use the received digitized temperature representative signals to execute the first and / or second algorithm, if these algorithms contain temperature dependent parameters. Likewise, the system is provided with a motion detector 34, the signals of which are supplied to the first computer unit 26 for further processing in the same way as described for the temperature sensor. In general, it holds that the information obtained with the additional sensors can be used for making software-based corrections. However, it is also possible that the first computer unit generates feedback signals based on information obtained with the additional sensors, which, as described above, can be fed to various parts of the system for setting, for example, said parameters.

According to a very advanced embodiment of the invention, the system 1 is further provided with a second computer unit 38 to which output signals from the sensors 32, 34 are also applied. The second computer unit 38 processes these signals according to a third algorithm, which determines how adjustment parameters of, for example, the photomultiplier 6, pulse height analyzer 10 and / or A / D converter 14 can be adjusted via line 40. For example, the gain of units 6, 10, 14 can be adjusted temperature-dependent.

According to a very advantageous embodiment, the units 2, 6, 10, 14 and 18 are brought together in a housing 42 and form a probe. If the units 32, 34 and 38 are present, they can also be housed in the housing 42. This has the advantage that the probe can be directly adjusted and adjusted on the basis of the physical conditions of the direct environment of the probe measured by the sensors 32, 34.

The invention is not limited to the embodiments of system 1 shown in figure 1. Thus, on the one hand, the transmitter / receiver units 18, 22 can be replaced by a direct connection through line 44. On the other hand, the other lines of Figure 1 can be replaced by pairs of transmitter / receiver units. The A / D converter 14 could be part of the second computer unit 38. The system can also be part of a larger system, such as, for example, a mineral separation system. In such a separation system, a base stream of matter is often split into a first stream comprising minerals of a first kind and a first residual group. The first residual group can then be split into a second stream comprising minerals from a second soorb and a second residual group, etc. With the aid of the system 1, for example, it can be determined from the basic stream how many minerals of the first type are present therein. On the basis of this information, process parameters (such as the speed of the base current) of the separation system can be set. In addition, the system 1 of the first residual group can be used to determine how many minerals of the second type are present therein. On the basis of this information, process parameters of the separation system can also be set, etc. It can also be checked whether, for example, the flow with minerals of the first type is not "contaminated" with other minerals.

The software of the first and second computer unit is preferably provided with a protection against unwanted copying thereof.

To illustrate this, it will be further indicated on the basis of figure 3 from which process steps the first and second algorithm can be constructed.

in Figure 3, an operation is represented by a circle and data by a square.

From the input data 61, the data of the other sensors are continuously selected and processed 63. The processed data 65 can be output. From the input data 61, the detector data is also continuously selected and sorted 67 and collected in a spectrum 69. Once per second or as much longer as desired, this spectrum is converted 71 to another spectrum 73, in which the measured photons are sorted by energy . This is done with a number of conversion factors 75. From this spectrum 73, concentrations 77 of potassium, uranium and thorium are calculated 79 using previously recorded spectra of K, U and Th separately and a background spectrum 81. Energy stabilization 83 is obtained by concentrations 77 and spectra 81 compose a spectrum and compare it with spectrum 73 and adjust conversion factors 75 accordingly. This stabilization is entirely software-based. Mineral or mineral group ratios 85 are calculated from the K, u and Th concentrations 77 using previously determined radiometric data for these minerals 89.

Calculation 79 of concentrations 77 can be performed as follows.

Hereafter it holds that: S (i) = number of photons detected per second detected with energy Ei in matter to be analyzed;

Cx = concentration of nuclide x in matter to be analyzed; X (i) = K (i), U (i), Th (i): number of photons detected per second with energy Ei from pure K, U or Th spectra; B {i) = number of photons detected per second with energy Ei from background radiation; i = 1, 2 .... n; and x = K, U or Th.

The values of K (i), U (i), Th (i) and B (i) are predetermined.

The value of Ck, Cu and C <rh can be determined by the least squares method.

This means that:

(1) where

represents the uncertainty in the number of photons detected with energy Ei in the time interval T.

From formula (1), C ^, Cu and 0¾ can be determined. It is noted that formula (1) can also be applied by using only part of the spectrum. Therefore, not all values of i are used. Preferably, those values of i are then used for which Ei is in or near a peak.

The calculation of 87 can be performed as follows.

It is assumed here that the matter to be analyzed comprises four groups of minerals, which are indicated with a, b, c and d. Each mineral group is characterized by its relative mass nij in the matter and three concentrations of Cj (u),

Cj (Th) and Cj (K) with j = a, b, c or d.

The relative masses are characteristic of the matter to be analyzed, while the concentrations (Cj (U), Cj (Th) and Cj (K)) are characteristic of the mineral group. These latter concentrations are therefore known. A mineral group is a predefined group of minerals whose spectra are very similar. However, a mineral group can also consist of only one type of mineral. The mineral groups are further defined in such a way that the spectra of different mineral groups are not very similar.

For the matter, C (U), C (Th) and C (K) represent the total (activity) concentrations of U, Th and K. These values can be determined according to formula (1), furthermore it holds that: maCa (U) + mbCb (U) + mcCc (U) + m <aCd (U) = C (U) maCa (Th) + 11¾¾ (Th) + mcCc (Th) + (Th) = C (Th) (2) maCa (K) + mbCb (K) + mcCc (K) + mdCd (K) = C (K) ma + mb + mc + md = l

From the equation (2), with the known values of Cj (U), Cj (Th) and Cj (K) and the measured values of C (ü), c (Th) and C (K), the values of ma, mb, rric and are determined.

On the basis of the values of ma, 1%, me and 11¾ it is now known in what quantities the mineral groups a, b, c and d are present in the analyzed matter.

Claims (22)

System for determining a composition of radio-nuclides in, for example, a mineral-containing matter by detecting gamma and / or X-rays emitted by the nuclides, provided with a detector unit which emits an electrical signal containing information about the intensity and energy of the emitted radiation and a signal processing system with which these electric signals are further processed to determine said composition, characterized in that the signal processing system comprises an A / D converter to which said electric signals are supplied and a first computer unit which further processes signals output by the A / D converter to determine said composition. System according to claim 1, characterized in that the detector unit comprises a scintillation detector and a photomultiplier which converts the light pulses delivered by the scintillation detector into an electric pulse with an amplitude which is a measure of the energy of the radiation received by the scintillation detector. System according to claim 2, characterized in that the detector unit is further provided with a pulse height analyzer for obtaining said electrical signals. System according to claim 1, characterized in that the detector unit comprises a semiconductor crystal to which a bias voltage is applied and means for detecting a variation in the bias voltage for obtaining said electrical signals. System according to any one of the preceding claims, characterized in that the first computer unit composes an energy spectrum of the detected radiation from the signals supplied by the A / D converter. System according to claim 5, characterized in that the first computer unit determines the concentration of the radionuclides on the basis of the spectrum according to a predetermined first algorithm. System according to claim 6, characterized in that the first computer unit determines said concentrations on the basis of the entire determined spectrum. System according to claim 6, characterized in that the first computer unit determines said concentrations on the basis of predetermined energy regions of the spectrum corresponding to spectra of individual radionuclides whose concentration is determined. System according to any one of claims 6-8, characterized in that the first computer unit is provided with a memory in which energy spectra of radiation emitted by radionuclides are stored. System according to claim 9, characterized in that the spectra stored in the memory are used in the predetermined first algorithm. System according to any one of claims 6-10, characterized in that the first computer unit determines the composition of the matter in minerals on the basis of said concentrations according to a predetermined second algorithm. System according to any one of claims 5-11, characterized in that data of minerals known per se and the associated concentrations of radionuclides are stored in the memory of the first computer unit. System according to claims 11 and 12, characterized in that the second algorithm uses the information about said minerals stored in the memory. System according to any one of the preceding claims, characterized in that the detector unit is provided with sensors with which sound, temperature, magnetism and / or other physical phenomena in the vicinity of the nuclides to be detected can be detected and converted into an electrical sensor signal. System according to claim 14, characterized in that the sensor signal is supplied via the A / D converter to the first computer unit for making corrections when determining said composition. System according to claim 15, 6 and / or 11, characterized in that said corrections are carried out by software. System according to any one of claims 14-16, characterized in that the sensor signal is supplied to a second computer unit for correcting and / or stabilizing the detector unit. System according to any one of the preceding claims, characterized in that the system further comprises a transmitter unit to which output signals from the A / D converter are applied and a receiver unit which supplies received signals to the computer unit. System according to any one of the preceding claims 1-17, characterized in that the output signals of the A / D converter are supplied to the computer unit via a cable. System according to any one of the preceding claims, characterized in that the detector unit and the A / D converter are housed in a probe-forming housing. System according to claims 17 and 19, characterized in that the second computer unit is also housed in said housing. System according to claim 2, characterized in that the scintillation detector comprises a BGO crystal.